1. Technical Field
The present technology pertains generally to magnetic resonance diagnostic schemes and more particularly to an NMR based method for determining the oil and water composition in drilling mud by separating out signals from oil and water in a two dimensional relaxation space wherein the oil and water ratio is a function of the separated out signals.
2. Background
In the exploration of oil or gas by drilling, a drilling fluid or mud is circulated in the bore hole to cool and lubricate the drill bit, move drill cuttings away from the drill bit and to the surface for removal, maintain the integrity of the wellbore and to create a counterbalance hydrostatic pressure to prevent well blowouts. Circulation of drilling muds to the drill bit and back to the surface can often take several hours to complete.
The drilling fluid may accumulate water from geological formations or from the surface as drilling progresses and the drilling fluid completes its circuit through the wellbore. The water content of the drilling mud composition is monitored, in part, to ensure that the hydrostatic pressure imposed by the drilling mud exceeds the formation pressure of the well.
Drilling fluid is a complex mixture of liquids, solids and additional chemicals. This is most often an emulsion either a water-in-oil or oil-in-water emulsion. The range of components in drilling mud is extremely broad and may include water, oil, soluble salts, viscosity modifiers (e.g., emulsifiers, viscosifiers) and other chemicals and solids that are added to control the physical and chemical properties of the mud. Materials that may be added to drilling fluids include synthetic based oils, diesel fuel, lime, calcium chloride, Bentonite, barite, biocides, and other similar materials. The properties of the drilling mud or fluid are defined by the drilling requirements and the mud engineer makes the decision based on the physical and chemical analysis of the drilling mud as well as from personal knowledge of the drilling operation.
In addition to the purposeful addition of compounds or materials to the mud, there will be drill cuttings that are accumulated in the mud over time as the well is drilled. Drill cuttings are any material that is extracted from the borehole during the drilling operation. Drill cuttings have a wide range of components and could include granite, gypsum, clay, dolomite, chalk, quartz, sand, sulfur, sandstone, shale as well as other minerals, rocks and salts, depending upon the underground formations that are drilled.
The general water and oil volume percent measurement of drilling mud is conventionally performed by using a retort. A set volume of drilling fluid is placed in the retort and the oil and water phases are then distilled off of the sample. The solids remain and the oil and water fractions are collected in a graduated cylinder. The volumes of the oil and water phases are then read directly off of the scale of the graduated cylinder and can be reported as a ratio, a volume percent of water or a volume percent of oil. This measurement procedure is slow and can only be performed on a small volume of the sample of drilling material.
Distillation apparatuses such as retorts are typically used to measure the oil and water compositions in drilling muds, but these devices are time consuming to operate and clean. One NMR relaxometry based approach uses solely T2 measurements. A weakness with T2 measurement techniques is possible overlap of the peaks that are attributed to oil and water. A method to get around this is to “deconvolute” the peak by looking at the second derivative of the peak to determine a cutoff for oil and water. This is problematic as this requires the peak to have a shoulder in order to partition the peak.
A second NMR based method involves adding a paramagnetic ion to the drilling mud which shifts the water signal from the overlapped peak to a shorter relaxation time. This is problematic for solutions where the overlapped peak is already at a very short relaxation time. The added paramagnetic ion shifts the signal from the water in the overlapped peak to a lower relaxation time resulting in a signal that cannot be measured using current detection techniques. However, adding a paramagnetic ion is not practical for in-line and on-line determination of water and oil fractions in a stream of drilling mud.
Accordingly, there is a need for efficient methods and materials for accurately and quickly analyzing drilling muds than is available with existing techniques. There is also a need for materials and methods that provide effective separations at low cost. The presently described technology satisfies these needs as well as others and is generally an improvement over the art.